1. Field of the Invention
The present invention relates generally to engine exhaust systems. In particular, to a circuit and control strategy method of providing power to an electrically heated catalyst without the inefficient exchange of energy between the engine battery and alternator.
2. Description of the Related Art
Typical vehicles have a catalyst placed downstream of the exhaust manifold in the exhaust system. One of the main purposes of the catalyst is to provide a means of purifying hydrocarbon and carbon monoxide emissions which may emanate from the engine. To perform such purification, most catalysts must be heated to a high temperature to reach optimal purification performance. This requires a waiting period approximately equal to the time required for the engine to reach a "warmed up" or steady state operating condition. The catalyst is thereby brought within operating temperature by the heat of the exhaust emanating from the engine. In addition, engines may sometimes run rich during warm-up. This further inhibits purifying reactions since an adequate supply of oxygen is not present. By the time the catalyst temperature has reached operating level, hydrocarbon emissions may have escaped the engine exhaust system without being fully purified.
Prior engine exhaust systems, which have implemented electrically heated catalysts, have not dealt effectively with real world power constraints. Engine batteries and start capacitors have been used to supply power directly to the catalyst. This has resulted in undue power strain being placed on the battery.
It is therefore desirable in the art of engine exhaust systems to provide a method and apparatus which will quickly bring a catalyst within a peak operating range soon after the engine is started without producing undue strain on the engine battery.